We checked out the Ultimate Marvel vs. Capcom 3 panel yesterday at Comic-Con and got some juicy details on the game:
1. The game will be coming with reversible packaging, which means two covers (American and Japanese). 
2. Pre-Order DLC Costume Packs will be available from Gamestop, Best Buy and Amazon.
3. New stages are "City That Never Sleeps" and "Days of Future Past."
4. New opening CG movie was shown (Deadpool can be seen surfing on Phoenix Wright's "OBJECTION!!!" quote bubble. 
5. Galactus is playable. 
6. Rocket Raccoon trailer will be something special. Frank West also coming soon. 
7. New game mode - "Heroes and Heralds" Mode.
Players can either choose to save the earth by playing with the good guys or destroy it by playing with Galactus' silver clones. Conquer different areas with your team in offline mode and unlock a bonus stage. Start clans online with other players. One week online campaigns will be available from Capcom.
100 different special ability cards are available to players, which will also sport the likenesses of several Marvel and Capcom characters. Howard The Duck will even be one of the cards. Some of the abilities seen are double jump, extra armor, invincibility towards projectile attacks and the parry system seen in Street Fighter 3: 3rd Strike. This will be available as free post launch DLC.